Question: Given the line: $-x - 3y = 21$ What is the $y$ -intercept?
Solution: The $y$ -intercept is the point where the line crosses the $y$ -axis. This happens when $x$ is zero. Set $x$ to zero and solve for $y$ $ -1(0) - 3y = 21 $ $-3y = 21$ $\dfrac{-3y}{-3} = \dfrac{21}{-3}$ $y = -7$ The line intersects the $y$ -axis at $(0, -7)$. ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${10}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ ${\llap{-}10}$ ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${10}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ ${\llap{-}10}$ $(0, -7)$